fix(managed-backfills): Add clarity to slack notifications (#2091)

* fix(managed-backfills): Add clarity to slack notifications

* Update dags/bqetl_backfill_complete.py

Co-authored-by: Alexander <anicholson@mozilla.com>

---------

Co-authored-by: Alexander <anicholson@mozilla.com>

dags/bqetl_backfill_complete.py

@@ -49,7 +49,7 @@ with DAG(
             watcher_text = " ".join(
                 f"<@{watcher.split('@')[0]}>" for watcher in entry["watchers"]
             )
-            return f"{watcher_text} :hourglass_flowing_sand: Completing backfill of `{entry['qualified_table_name']}`. A snapshot of the current production data will be kept as a backup."
+            return f"{watcher_text} :hourglass_flowing_sand: Completing backfill of `{entry['qualified_table_name']}` has started - currently swapping backfill data into production. A snapshot of the current production data will be kept as a backup. You will receive another notification once the completing step is done."
 
         notify_initiate = SlackAPIPostOperator(
             task_id="slack_notify_initate",

dags/bqetl_backfill_initiate.py

@@ -49,7 +49,7 @@ with DAG(
             watcher_text = " ".join(
                 f"<@{watcher.split('@')[0]}>" for watcher in entry["watchers"]
             )
-            return f"{watcher_text} :hourglass_flowing_sand: Initiating backfill scheduled for `{entry['qualified_table_name']}`."
+            return f"{watcher_text} :hourglass_flowing_sand: Initiating backfill scheduled for `{entry['qualified_table_name']}`.  You will receive another notification once the backfill is done."
 
         notify_initiate = SlackAPIPostOperator(
             task_id="slack_notify_initate",